1. Field of the Invention:
The present invention relates to the treatment of the thermosetting polyurethane surface of a sheet or film having antilaceration and self-healing properties, with the sheet or film, having and exposed transparent sheet or film of thermosetting polyurethane, being employed as an external layer on a laminated glass sheet or laminated plastic sheet. Further, the surface to be treated has deposited thereon a solution or emulsion of wax containing a silicone oil. Also included in the present invention is a sheet or film treated by the process of the invention.
2. Description of the Prior Art:
The terminology "sheet or film having antilaceration properties" refers to a sheet or film which, in the case of breakage of a glass pane, resists laceration and covers the sharp edges of the glass fragments, thereby protecting the vehicle occupants from cuts and injuries. The terminology "sheet or film having self-healing properties" refers to a sheet or film which is self-occluding, whereby accidental chafes, scratches or local compressive indentations on the surface of the sheet or film quickly and automatically disappear. In other words, the sheet or film is scatch-resistant and abrasion-resistant.
When a transparent polyurethane sheet or film is employed to cover a glass sheet, it automatically serves to protect against lacerations and it is desired that it be scratch resistant.
U.S. Pat. No. 3,971,864 describes the use of a wax layer to coat a sheet or film of thermoplastic polyurethane having antilaceration properties and covering a sheet of silicate glass, wherewith following the coating process the wax layer is polished. The substrate to which this treatment is applied comprises, e.g., a polyurethane sheet or film having antilaceration properties described in U.S. Pat. No. 3,808,077. These thermoplastic polyurethanes are produced from low molecular weight components which over a period of time diffuse toward the free surface of the antilaceration layer where they form a grayish white precipitate or deposit. The treatment of the surface with a wax prevents or impedes the formation of this detrimental precipitate, or if the precipitate has already formed then the treatment causes it to disappear.
The wax-based polishes employed according to this patent comprise aliphatic hydrocarbons as solvents for the wax or wax-like substance, and further comprise various amounts of silicone oils as glossing agents.
It is difficult to obtain a wax layer free from (and unsusceptible to) striae and other optical perturbations. Furthermore, it is well-known that after a non-uniform film is formed, optical defects in it cannot be completely eliminated even by repeated mechanical polishing. At most, they may only be relieved.
Moreover, when the wax solution or dispersion described in U.S. Pat. No. 3,971,864 is applied to a thermosetting sheet or film of polyurethane having antilaceration properties (such as the sheets or films described in French Pat. No. 2,251,608), new problems are created; in particular, the surface of the polyurethane sheet or film is streaked by the wax solution.
Hence, a need clearly continues to exist for a treatment for the surface of a sheet or film having antilaceration properties, where the sheet or film essentially entails a transparent polyurethane material, which does not impair the optical properties of the safety glass with which the treated film is employed.